Conodonts are extinct chordates resembling eels, classified in the class
Conodonta. For many years, they were known only from tooth-like microfossils
found in isolation and now called conodont elements. Knowledge about soft
tissues remains limited. The animals are also called Conodontophora to avoid
ambiguity. Conodont teeth are the earliest found in
the fossil record. Description
The 11 known fossil imprints of conodont animals record an eel-like creature with
15, or more rarely, 19 elements that form a bilaterally symmetrical array in
the head. This array constituted a feeding apparatus that is radically
different from the jaws of modern animals. The three forms of teeth, i.e.,
coniform cones, ramiform bars, and pectiniform platforms, may have
performed different functions. The organisms range from a centimeter or
so to the large Promissum, 40 cm in length. It is now widely agreed that
conodonts had large eyes, fins with fin rays, chevron-shaped muscles and a
notochord. The entire class of conodonts is
postulated to have been wiped out in the Triassic–Jurassic extinction event,
which occurred roughly 200 million years ago.
Ecology The "teeth" of some conodonts have been
interpreted as filter-feeding apparatuses, filtering plankton from the
water and passing it down the throat. Others have been interpreted as a
"grasping and crushing array". The lateral position of the eyes makes it
unlikely that conodonts were active predators. The preserved musculature
suggests that some conodonts were efficient cruisers, but incapable of
bursts of speed. Classification and phylogeny
As of 2012, scientists classify the conodonts in the phylum Chordata on the
basis of their fins with fin rays, chevron-shaped muscles and notochord.
Milsom and Rigby envision them as vertebrates similar in appearance to
modern hagfish and lampreys, and phylogenetic analysis suggests they are
more derived than either of these groups. However, this analysis comes
with one caveat: early forms of conodonts, the protoconodonts, appear to
form a distinct clade from the later paraconodonts and euconodonts.
Protoconodonts likely represent a stem group to the phylum that includes
chaetognath worms; this conclusion suggests that chaetognaths are not close
relatives of true conodonts. Moreover, some analyses do not regard conodonts as
either vertebrates or craniates, because they lack the main characteristics of
these groups. Elements
For many years, conodonts were known only from enigmatic tooth-like
microfossils, which occur commonly, but not always in isolation, and were not
associated with any other fossil. These phosphatic microfossils are now termed
"conodont elements" to avoid confusion. They are widely used in biostratigraphy.
Conodont elements are also used as paleothermometers, a proxy for thermal
alteration in the host rock, because under higher temperatures, the phosphate
undergoes predictable and permanent color changes, measured with the
conodont alteration index. This has made them useful for petroleum exploration
where they are known, in rocks dating from the Cambrian to the Late Triassic.
Until the early 1980s, conodont teeth had not been found in association with
fossils of the host organism, in a konservat lagerstätte. This is because
most of the conodont animal was soft-bodied, thus everything but the
teeth was unsuited for preservation under normal circumstances.
The conodont apparatus may comprise a number of discrete elements, including
the spathognathiform, ozarkodiniform, trichonodelliform, neoprioniodiform, and
other forms. See also
Lau event - mass extinction event with major impact on conodonts
Notes References
Further reading Aldridge, R. J.; Briggs, D. E. G.;
Smith, M. P.; Clarkson, E. N. K.; Clark, N. D. L.. "The anatomy of conodonts".
Philosophical Transactions of the Royal Society of London, Series B 340:
405–421. doi:10.1098/rstb.1993.0082. Aldridge, R. J.; Purnell, M. A.. "The
conodont controversies". Trends in Ecology and Evolution 11: 463–468.
doi:10.1016/0169-5347(96)10048-3. PMID 21237922.
Donoghue, P. C. J.; Forey, P. L.; Aldridge, R. J.. "Conodont affinity and
chordate phylogeny". Biological Reviews 75: 191–251.
doi:10.1017/S0006323199005472. PMID 10881388.
Gould, Stephen Jay. "Reducing Riddles". In The Flamingo's Smile, 245-260. New
York, W.W. Norton and Company. ISBN 0-393-30375-6.
Janvier, P. "Euconodonta". The tree of life web project, http:tolweb.org.
Retrieved 2007-09-05. Knell, Simon J. The Great Fossil Enigma:
The Search for the Conodont Animal 440 pages
Sweet, Walter. The Conodonta. Sweet, W. C.; Donoghue, P. C. J..
"Conodonts: past, present and future". Journal of Paleontology 75: 1174–1184.
doi:10.1666/0022-3360(2001)0752.0.CO;2. ISSN 0022-3360.
External links Mark Purnell. "An oblique anterior view
of a model of the apparatus of the Pennsylvanian conodont Idiognathodus".
"'The Jaws That Catch': an Introduction to the Conodonta". Palæos. Retrieved
2013-07-01. Jim Davison. "Ordovician conodonts".
Retrieved 2009-07-07.